According to the prior art, a cutting saw in a multi-purpose machine, especially in harvester and processor multi-purpose machines, is formed of a hydraulic motor and a cutting flange or cutting disc. The drive sprocket of the hydraulic motor rotates an endless chain around a flange, and the feed of the flange against the tree generally takes place by means of a hydraulic cylinder. In a disc saw, the motor rotates a disc directly or with the aid of a ring gear. In these too, the feed against the tree takes place by means of a hydraulic cylinder.
A problem in devices according to the prior art is the difficulty of adjusting the feed. The size and hardness of wood varies and additionally, for example, knots are extremely hard. In addition, the condition of the blade of the cutting device is decisive. A sharpened blade will cut considerably better than one in poor condition.
Nowadays, the simplest practicable control is based on a throttle installed on the motor's return line. While the motor rotates, pressure to the hydraulic cylinder intended for the flange feed is obtained with the aid of the throttle. The higher the speed of the motor, the greater is the feed pressure. When the motor stops, the pressure effect ends.
In order to operate, such a system demands that the return oil be throttled to about 50 bar. When the operating pressure is about 200 bar, 25% of the output of the saw motor will be lost as heat. The feed control can also be performed on the pressure side of the motor. This generally takes place with the aid of a pressure-reduction valve and a valve throttling the cylinder's speed. This works well in standard conditions, but when the hardness of the wood increases the chain tends to stop, as the feed pressure cannot take the rotation of the motor into account. In order to get a cutting saw to operate, the throttle is used to adjust a suitable approach speed for the cutting device while the pressure during sawing is regulated by a pressure valve. In practice, it is extremely difficult to adjust the throttle with hard wood and a worn cutting device. The solution generally used is to over-dimension the hydraulic motor, i.e. in practice the dimensioning of the hydraulic motor is doubled.
A sufficient pressure is required for the proper cutting of wood (for example, time, no tearing). In theory, the diameter of the cylinder of the feed device could be increased, but this would lead to large flow amounts in the cylinder line, as normal sawing lasts for about 1-2 s.
A system is known from publication WO 01/84910, in which the operation of the hydraulic cylinder and the cutting saw is controlled with the aid of a computer. However, such a system is extremely labourious and expensive to implement, as the system requires several measuring sensors and a computer.